1. Field of the Invention
The present invention relates to a channel code converter, to a channel coding system therefor, and to a recording medium recording an encoding control program. The present invention is particularly adapted to digital recording disk devices such as an optical disk device, a magnet-optic disk device, a phase-change disk device and a hard disk device, and to a digital recording VTR (video tape recorder).
2. Description of the Prior Art
In a digital recording disk device, digital data are recorded in a digital form not directly but after the data are encoded. This also applies to recording video and audio data in a digital form in the digital recording VTR. A representative example of a channel code used in encoding the data may be a (1,7) code.
FIG. 1 shows a code conversion table of the (1, 7) code. In FIG. 1, two data bits are converted into 3 channel bits, and are then recorded according to an NRZI (non-return to zero inverse) rule. FIG. 1 further illustrates an example of recording according to the NRZI rule after 4 data bits are converted into 6 channel bits. The NRZI rule is the one in which a bit is inverted with "1" and is recorded, and a bit is not inverted with "0" and is recorded.
The (1, 7) code may cause deviation in the decoded pattern due to an error at the time of recording/reproduction. By taking the return of this case into consideration, a synchronization signal is inserted every after several hundred to several thousand bits. The synchronization signal uses a channel bit pattern that does not appear in the normal data to make a clear distinction over the data.
Characteristics of the channel code are generally evaluated in terms of a minimum inversion interval Tmin, a maximum inversion interval Tmax, a detection window width Twin, and a DC (direct-current) component. It is desired that the minimum inversion interval Tmin is great and (Tmax/Tmin) is small. It is further desired that the detection window width is great and the DC component is free or is small as much as possible.
The (1, 7) code has a minimum inversion interval Tmin=1.33T, a maximum inversion interval Tmax=5.33T, a detection window width Twin=0.67T, and the DC component which is not free. The (1, 7) code has an advantage in that the minimum inversion interval Tmin and the detection window width Twin are large, and the maximum inversion interval Tmax has a normal value. However, the (1, 7) code has a defect in that the DC component is not free. As described above, a suitable channel code is required for a recording system which requires free DC.